page_title: Crankset
section_title: Rotor Box System
hierarchical_section_title: Crankset / Variations / Rotor Box System
caption_attribution_description: English: Rotor crankset with Q-rings
context_page_description: The crankset or chainset, is the component of a bicycle drivetrain that converts the reciprocating motion of the rider's legs into rotational motion used to drive the chain or belt, which in turn drives the rear wheel. It consists of one or more sprockets, also called chainrings
  or chainwheels attached to the cranks, arms, or crankarms to which the pedals attach. It is connected to the rider by the pedals, to the bicycle frame by the bottom bracket, and to the rear sprocket, cassette or freewheel via the chain.
context_section_description: Rotor is a trade name of a type of crank used in the transmission system of a bicycle. The Rotor crank was developed by Aeronautic Engineering School students in Madrid, Spain in 1995 and was later commercialised. While Rotor Box found success with recreational road and mountain cyclists, many competitive cyclists continue to use the traditional fixed system as offered by major manufacturers Campagnolo and Shimano, amongst others.  One major factor is weight— the Rotor Box System is 50%–75% heavier than most competitive cranks.  Other negative factors include higher purchase cost than other fine cranksets, and increased maintenance due to the complexity of the system.  These cranksets are no longer in production, and availability of some parts is problematic.  However the bearings are standard parts.  A few parts, like links, are still distributed.
  This system originated as a cog-driven internal mechanism inside a purpose built bicycle's bottom bracket. In this first "ROTOR Box" design, the drive-side crank had an offset chainring spider with round rings. The drive side crank's gear ratio varied during the pedalling cycle by moving the round chainring upward and downward in regards to the crank's axle. The non-drive side crank was accelerated and decelerated by a gearing mechanism inside the bottom bracket to mimic the gear ratio variation the drive side crank went through, at an exact 180 degree phase-offset. While highly effective mechanically, these bicycles were costly and the significant movement of the chainring made shifting quality problematic.
  Later generation ROTOR System cranks moved the mechanism into an orbital chainring spider with a fixed rotational axis. These "ROTOR System" cranksets fit into classic BSA and ITA bicycle frames. Unlike a standard pair of cranks that always remain at 180 degrees relative to each other, the ROTOR system varies this angle through the circle of motion. The left and right crank arms speed up and slow down independently, relative to the chainrings during the pedalling cycle. The mechanism causing this is designed by ofsetting the axis of rotation of the crank spindle and spider, then connecting the spider to the individual crank arms via two independent links.
   As the crank rotates, the distance between the axle and spider varies. By placing a pivot point on the crank arm and the spider and connecting these via linkages, the varying axle to spider distance pivots the linkages up and down, pushing the cranks forward and pulling them backward relative to the chainrings during the rotation. This increases and decreases the effective gear the cyclists' two legs push as the crankset rotates. The effect of these movements eliminates the dead spot (where little power is produced) at the top and bottom of the pedaling cycle, and reduces knee strain. The manufacturer claims that power output relative to heart rate is increased, amongst other claimed benefits.
  It takes a couple of weeks of regular use to become accustomed to the unusual feel of the Rotor linkage cranksets.  After becoming accustomed to it, most riders prefer it.  However, there is no difficulty in switching between ordinary cranksets and Rotor linkage cranksets.  Once a rider has learned to use Rotor linkage cranksets the adaption when switching back and forth between crankset types only takes a minute or two.
  Many competitive cyclists, including the Cervélo TestTeam, use Rotor's Q-rings which mimic the fluctuation in gear size without the added weight. However Rotor Q-rings and other non-round rings cannot duplicate the crank arm movements that allow application of power through the dead spots of the pedaling cycle.  Non-round rings also increase the difficulty of setting up the front derailleur, while Rotor linkage cranksets present no extra difficulty in that regard.
caption: Rotor crankset with Q-Rings
exif: {"Image Make": "Motorola", "Image Model": "MB300", "Image XResolution": "72", "Image YResolution": "72", "Image ResolutionUnit": "Pixels/Inch", "Image DateTime": "2011:06:20 11:04:14", "Image YCbCrPositioning": "Centered", "Image ExifOffset": "174", "Image GPSInfo": "358", "Thumbnail Compression": "JPEG (old-style)", "Thumbnail XResolution": "72", "Thumbnail YResolution": "72", "Thumbnail ResolutionUnit": "Pixels/Inch", "Thumbnail JPEGInterchangeFormat": "458", "Thumbnail JPEGInterchangeFormatLength": "7855", "EXIF ExifVersion": "0220", "EXIF DateTimeOriginal": "2011:06:20 11:04:14", "EXIF DateTimeDigitized": "2011:06:20 11:04:14", "EXIF ComponentsConfiguration": "YCbCr", "EXIF FlashPixVersion": "0100", "EXIF ColorSpace": "sRGB", "EXIF ExifImageWidth": "2560", "EXIF ExifImageLength": "1920", "Interoperability InteroperabilityIndex": "R98", "Interoperability InteroperabilityVersion": "[48, 49, 48, 48]", "EXIF InteroperabilityOffset": "328"}